rxspeed87

as soon as I get the car up and running again I am going ot have a true dual setup on the car
so far from what it looks like I am going ot have the mindtrain dual out header with 2 inch pipes all the way back till the muffs then have it go to 2 1/2 inch piping to fit the N1 cans out back ( still debating if I should bring the pipe up to 3 1/2 though I doubt it. I was curious though if at the point where the stock system would Y off into the dual setup if I could put a x-pipe like a lot of mustangs have or maybe just put a equalizer tube that should go in there
that way it is still a dual setup but it would equalize the pressure between the two sides of the motor.
I know on a piston motor from some dyno runs where that was the only mod there have been big gains
anyone have any ideas out there?

Scott 89t2

I don't think so...

rxspeed87

why would you say no.
kinda looking for a reason as to why it would or would not work

Scott 89t2

cause if it worked it would come like that... racing beat systems are sweet and they put R&D into it. if that worked better it would come like that. the rotary produces exhaust pulses different then a car since there are no vavles in the way. and you want those pulses to be untoched by each other.

RETed

Scott 89t2 is right - Racing Beat has done a lot of R&D into their NA exhaust systems, and their conclusion is that a totally separate exhaust system for front and rear rotor all the way out back makes the best power.&nbsp Now, I'm not going to go into why this is so (go ask Racing Beat yourself?), but rotary exhaust pulses and piston exhaust pulses are two different beasts.&nbsp For one, a rotary exhaust pulse is a lot stronger (a magnitude of at least 2-4 times) than a piston exhaust pulse.&nbsp A complete engine cycle on a 4-cylinder or V-8 is going to see 4 exhaust pulses every 90-degrees; a rotary will spit out it's front and rear exhaust pulses every 180-degrees of each other.

An H-pipe or X-pipe crossover is a waste of time and money for a rotary.&nbsp Yes, I agree it works nicely on V-8's, but it doesn't apply for these cars.


-Ted

Evil Aviator

The purpose of a balance pipe (ie H-pipe, X-pipe, etc.) is for the two pipes to feed off each other's gas velocity when at low vacuum levels, which increases mid-range power without greatly reducing the top end. This setup has been shown to work in some V-8's, but nobody has ever had good results with this on a rotary.

IMO Racing Beat has the best balance between performance, price, and noise supression.

BlackRx7

I have a H crossover on my true dual setup, I notice a large gain in low end torque after i got it put on, plus I don't have any presilecers and it muffles it and gives it a lower agressive tone.

CivicV10@18000rpm

Doesn't a common 4 stroke 4 cylinder motor at 1000rpm have the same number of exhaust pulses as a 2 rotor 13B per "crank shaft revolution" at 1000rpm? Remember the rotors are actually spining 3 times slower than the crankshaft...right?

I agree the H-pipes and Y-pipes were designed for piston engines that have 2 banks of cylinders like V6's, V8's etc.

RETed

Lesse...4-cylinder...one revolution of the crank will spit out only one exhaust pulse.&nbsp One revolution of a 13B will spit out 1.5(?) exhaust pulses...well, it'll catch two of them:&nbsp one from the front and one from the rear.

Remember also that rotary engine exhaust pulse are a lot stronger than piston exhaust pulses.



-Ted

RETed

Uh, okay...



-Ted

CivicV10@18000rpm

But if you break it down a 4cyl has the same exhaust pulses or power strokes as a 13B 2 rotor. Let me explain. A single 4 stroke piston engine will produce 1 exhaust pulse per every 2 rev of the crank...correct? If you have a 2 cyl engine 4 stroker it will produce 2 pulses per 2 revs which is 1 pulse per 1 rev. Which a single piston 2 stroke does. Coincedentally a single rotor engine will produce 1 pulse per 1 rev with the rotor spinning at 1/3 the speed of the crankshaft...same as the 2 cylinder 4 stroker and 1 cylinder 2 stroker. http://www.howstuffworks.com/rotary-engine3.htm If you look at the eccentric shaft's lobe...it travels at the same speed as the crank shaft. If you look carefully you can time the eccetric shafts lobe with the exhuast pulse or the power stroke. The rotor spins 1/3 slower. Now with 2 rotors exhaust pulses are 2 per rev. Exactly the same as a 4 stroke 4 cyl.

Yes I knew about the stronger and hotter exhaust pulse of the rotary. Didn't mazda design the turbine blades a little differently to take advantage of that?

defylogik

i got a buddy that races rx7s in the scca.. hes building his now.. and he created a true dual exaust system for the car.. i guess it does wonders because he knows what he is talking about. he owns a machine shop that makes wind tunnels and also does dyno tuning for exhaust back pressures/ etc for his jet and turbine engines.

he will hook up a motor and put adjustor valves in the exhaust and then dynos the motor and then he can adjust where the bends should be best placed, etc.. pretty interesting stuff..

scott

mazdaspeed7

A crossover pipe will make the car quieter, and will make the sound deeper, and less chainsaw like. You WILL gain some bottom end at the expense of some top end. I dont have dyno experience to back up how much, etc, but the closer the crossover pipe is to the collector and the bigger it is, the more low end you will gain at the expense of top end.

Evil Aviator

If you want to stay in a happy mood, then don't ever put your car on a dyno. FYI you can't have a "true dual" (proper terminology = uncollected) exhaust if you have an H-pipe.

No, the 4-stroke 4-cylinder will spit out 2 exhaust pulses per crankshaft revolution. A 2-rotor engine will also spit out 2 exhaust pulses per e-shaft revolution. CivicV10 is correct on this.

Yes, and the rotary also doesn't have any valves, so a reversion wave will kill the rotary's performance, which is why a balance pipe doesn't work.

wankelhead

do you mean header?on a true dual,there would not be a collector.....right ?very interesting,i think.
d

mazdaspeed7

Oops, I dont know what the hell I was thinking. It should be "the clower the crossover pipe is to the *engine*..."

mazdaspeed7

Actually it does work, but the powerband for it working is much different than V8's. Rotaries gain less low end, and lose much more top end. it works, but not very well. The only thing it does do very well is quiet it down.

If reversion waves killed rotaries performance(strictly n/a's here, turbos have different rules), single exhausts would make substantially less power than true dual, but this is not the case. You true dual does make more power than single, but not a lot more.

Evil Aviator

Um, so basically you are saying that it doesn't work.

So what kind of "true dual" exhaust is on the 787B, Argo JM-19, DG3 and DLM?

mazdaspeed7

It does a better job of quieting the exhaust than making more power. I dont have any dyno proof to back it up, but Im sure the gains on a rotary simply dont compare to those on a V8. A balance pipe on a V8 makes a pretty large difference in low end, and doesnt really hurt top end. On rotaries, it wont gain as much low end as on a V8, and it loses more top end. Not saying it doesnt work, just saying it doesnt work as well.

And I am not familiar with the exhaust on the 787B or any of the others you listed. Care to enlighten me?

Evil Aviator

Hehehe, yeah, I was just wondering what kind of "true dual" or H-pipes these front-running cars were using.

mazdaspeed7

Holy ****, that looks like fun. All of those are rotary, too, arent they

Evil Aviator

Yeah, but they don't have H-pipes or "true dual" exhaust, so they don't make any power. Do you get my point yet?